Assessing potential vulnerability of coral reefs through functional groups of herbivores

• Fishing can have major influences on ecological processes on coral reefs. Overfishing of herbivores is particularly detrimental, generating ecosystem-wide impacts where algae overgrow corals and become the dominant benthic organism. This can result in altered ecosystem functioning and subsequently, loss of important ecosystem services. Knowing when important processes, such as herbivory, are becoming fragile is important because it can provide an opportunity for managers to avoid such undesirable ecosystem changes. This study investigates the impact of artisanal fishing on three important functional groups of herbivores (grazers, scrapers and bioeroders) on five coral-dominated reefs outside Zanzibar, Tanzania. Fishing pressure was assessed through interviews with households and fishermen and compared with ecological data for each of the three focal functional groups. The ecological status of the groups were assessed through analysis of species richness, -abundance, -biomass and demographic structure; variables relating to functional performance and in a wider sense ecosystem resilience. The results showed a negative correlation between fishing pressure and fish biomass, -abundance, and diversity. Moreover, fishing had a negative influence on the demographic structure of functional groups, particularly for bioeroders, manifesting as a skewness towards smaller individuals within species populations. Fishing pressure also correlated positively with sea urchin abundances suggesting a compensatory response within the guild of herbivores, which could explain the low abundances of macro algae on all of the investigated reefs. This study shows that artisanal fishing can have significant impacts on herbivores which may erode the resilience on coral reefs. Moreover, it illustrates how functional groups may help to expose potential vulnerability of coral reefs by mechanistically linking the diversity and identity of species to ecosystem processes.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

Marine ecology

Marin ekologi

naturresurshushållning

Natural Resources Management

Publikations- och innehållstyp

vet (ämneskategori)

ovr (ämneskategori)